Previously we have reported a series of gambogicacid's analogs and have identified a compound that possessed comparable in vitro growth inhibitory effect as gambogicacid. However, their target protein as well as the key pharmacophoric motifs on the target have not been identified yet. Herein we report that gambogicacid and its analogs inhibit the activity of IκB Kinase-beta (IKKβ) through suppressing